Adherence to effective cardiovascular disease (CVD) risk factor medications is associated with improved CVD risk factor control, fewer hospitalizations, and lower mortality in patients with diabetes. However, many patients are poorly adherent to medications, and there are persistent racial/ethnic and socioeconomic disparities in medication adherence. Traditional clinical trials of interventions to improve medication adherence are often resource-intensive, and focus exclusively on patient-level barriers to behavior change. Unsurprisingly, these trials have not led to sustainable, cost-effective approaches to improve adherence. Health system-level medication adherence interventions that can be implemented, scaled up, and sustained across a wide range of health care delivery settings are urgently needed. Delivering efficacious prescription drugs through existing mail order pharmacies can be considered a system-level approach to enhancing access to medications. Previous research using observational data has shown that mail order pharmacy use is associated with improved adherence to CVD risk factor medications, and with improved CVD risk factor control. Despite this evidence, and although mail order pharmacy use is potentially cost-saving to both patients and health plans, fewer than 25% of patients with diabetes use the mail order pharmacy to obtain their diabetes medications. Mail order pharmacy use is even lower among non- whites and patients with lower socioeconomic status. We propose a randomized encouragement trial to encourage use of existing mail order pharmacy services among diabetes patients with poor adherence to CVD risk factor medications and who only use retail pharmacies in 3 health care systems: Kaiser Permanente Northern California, Harvard Pilgrim, and Kaiser Permanente Hawaii. These combined systems include approximately 300,000 patients with diabetes with diverse racial/ethnic and socioeconomic backgrounds. Patients with no history of mail order pharmacy use will be randomized into 3 arms: 1) a standardized intervention to encourage mail order use and provide easily accessible information on how to access the service; 2) a personalized intervention that includes components of the standardized intervention as well as additional information tailored to patient-specific characteristics such as prescription regimens and individualized potential savings by switching to the mail order pharmacy; and 3) usual care. In addition to examining the impact of the intervention on medication adherence and CVD risk factor control, we will examine factors affecting the sustainability and dissemination of the intervention, assess the intervention's impact on utilization and health care costs, and determine whether the intervention's impact differs across racial/ethnic and socioeconomic subgroups. This research will provide a foundation for developing sustainable, system-level approaches to addressing medication adherence in diabetes patients that can be widely disseminated and implemented across a diverse array of health care systems.